This invention relates to a network device of a mobile communications system and to a method of managing the power of the network device. More particularly, the invention relates to a network device of a mobile communications system and to a method of managing the power thereof, wherein maximum transmission power of each communication channel is updated at any time based upon transmission power control, thereby improving efficiency of power use and making it possible to increase the number of subscribers accommodated.
As shown in FIG. 15, a base station transceiver subsystem (BTS) 1 for performing communication wirelessly with a mobile station 2 has an amplifier 1a, a radio unit 1b, baseband signal processors 1c1 to 1cn for executing multiple-channel baseband signal processing, an intraoffice control unit (BTSC) 1d and an interface 1e for interfacing a base station controller (BSC) 3.
The amplifier 1a amplifies sent and received signals. The radio unit 1b frequency-converts a high-frequency signal, which enters from an antenna via the amplifier 1a, to a baseband signal, and frequency-converts a baseband signal to a high-frequency signal and inputs the high-frequency signal to the antenna via the amplifier 1a. The baseband signal processors 1c1 to 1cn subject communication signals (various control signals, voice signals and data signals, etc.) of respective multiple channels to processing such as spreading and quadrature modulation and input the processed signals to the radio unit 1b. Further, the baseband signal processors 1c1 to 1cn subject communication signals of respective multiple channels that enter from the radio unit to processing such as quadrature detection, despreading and data demodulation and input demodulated data to the interface 1e. The latter executes N-channel signal multiplexing/demultiplexing processing and processing for signal conversion between a base station transceiver subsystem (BTS) and a base station controller (BSC). The intraoffice control unit 1d exercises various control operations such as call control, communication-channel set-up control and power management control.
Power management control by the intraoffice control unit 1d is performed as follows: Maximum transmission power of a communication channel is set beforehand depending upon such factors as transmission speed, voice call and data call, etc. When there is a request to set up a communication channel, the intraoffice control unit 1d determines whether it is possible to allocate the maximum transmission power to the communication channel, whose set-up has been requested, within allocatable power limits. If allocation is possible, the maximum transmission power is allocated to this communication channel and processing of this communication channel is assigned to any of the baseband signal processors 1c1 to 1cn. If allocation is not possible, then the intraoffice control unit 1d does not allocate transmission power and responds to the requesting side by indicating that channel connection is not possible. FIG. 16 illustrates a case where allocation of maximum transmission power to channels #0 and #1 is possible and the processing of channels #0, #1 has been assigned to the baseband signal processor 1c1.
With regard to transmission power control in the baseband signal processors 1c1 to 1cn, transmission power control of individual channels typified by closed-loop control is carried out on a per-channel basis. By virtue of transmission power control, actual transmission power becomes smaller the above-mentioned allocated maximum transmission power. FIG. 17 is a diagram useful in describing downstream-line closed-loop transmission power control of individual channels in a baseband signal processor. This diagram shows the components constituting one channel.
The baseband signal processor 1c1 has a spread-spectrum modulator 5a for subjecting transmit data to spread-spectrum modulation using a spreading code that conforms to the specified channel, and a power amplifier 5b for amplifying its input, which is obtained by subjecting the spread-spectrum modulated signal to processing such as quadrature modulation and frequency conversion, and transmitting the amplified signal to the mobile station 2 from an antenna. A despreader 2a in the receiver section of the mobile station 2 subjects a receive signal to despread processing and a demodulator 2b demodulates the receive data. A SIR measurement unit 2c measures the power ratio between the receive signal and an interference signal. A comparator 2d compares a target SIR with the measured SIR, creates a command which lowers the transmission power by a TPC (Transmission Power Control) bit if the measured SIR is greater than the target SIR, and creates a command which raises the transmission power by the TPC bit if the measured SIR is less than the target SIR. The target SIR is a SIR value necessary to obtain, e.g., 10−3 (error occurrence at a rate of one error per thousand times). The target SIR is input to the comparator 2d from a target-SIR setting unit 2e. A spreading modulator 2f subjects transmit data and the TPC bit to spread-spectrum modulation. Following spread-spectrum modulation, the mobile station 2 applies processing such as D/A conversion, quadrature modulation, frequency conversion and power amplification and transmits the resulting signal to the base station 1 from an antenna. A despreader 5c in the baseband signal processor on the side base station applies despread processing to the signal received from the mobile station 2, and a demodulator 5d modulates the receive data and TPC bit to control the transmission power of the power amplifier 5b in accordance with a command specified by the TPC bit.
Thus, the intraoffice control unit (BTSC) 1d and the baseband signal processors 1c1 to 1cn exercise power control but the power control by each is performed independently of the other without any cooperation between them. As a consequence, by virtue of transmission power control on a per-channel basis, transmission power stabilizes in a state in which it is less than the initial transmission power established at the time of channel set-up. As a result, even if surplus power is produced (see FIG. 16), no measures for dealing with this are taken in the prior art. Conventionally, therefore, power is allocated to each channel excessively and, hence, the number of multiplexed channels, i.e., the number of subscribers that can be accommodated, per base station diminishes.
Further, there are instances where power greater than the allocated maximum transmission power becomes necessary when communication conditions deteriorate. With the prior art, however, power in excess of maximum transmission power cannot be allocated. The problem that arises in this case is that communication quality cannot be improved.